Nowadays, there are several types of precision boring heads, or fine precision boring cartridges in the market. Each one has a mechanism to provide adjustment of the cutting edge. There are different types of mechanisms, as described in, for example U.S. Pat. Nos. 4,786,217, 5,316,417; 5,326,198; 8,028,435 and U.S. Published Application No. 2013/0071193. Each mechanism has their positive and negative aspects, as summarized below.
U.S. Pat. No. 4,786,217 describes a mechanism that is small, uses few parts, and is rigid because it uses elastic deformation to create a spring effect, which keeps parts in contact every time an adjustment is made. The disadvantages of this mechanism are:
(1) The force created by the deflectable part, through elastic deformation is not constant, thus the rigidity can vary along the adjustment range.
(2) Due to its shape, deflectable part can lose elasticity very fast, particularly if the tool works in the limit of the adjustment range for a long time.
(3) Graduations provided to allow reading of the adjustment made are very small, so difficult to see, thus the adjustment is not reliable unless an auxiliary measurement instrument is used, like a comparator.
(4) Adjustment screw can lose engagement with the base body if operator unscrew it more than necessary.
U.S. Pat. Nos. 5,316,417 and 5,326,198 describe a mechanism that is precise and do not require any additional instrument to assure the adjustment made. However, they are complex, use a lot of parts, and because of that, they are more expensive and have a size limit. Besides, the structure of the mechanisms is more likely to present clearance between parts, which causes a difference between the expected and real diameter in the first machined hole.
U.S. Pat. No. 8,028,435 relates to an electronic system to adjust the tool, in order to improve the reliability of the adjustments, by providing a display that shows the machined diameter. This system has the following problems:
(1) The electronic circuitry can fail due to contact with coolant.
(2) Engagement with the body is difficult because operator should assure simultaneous contact with the adjusting screw and electrical contacts.
(3) Needs a battery to work, so it is necessary to stock this item and someone to control the battery life in order to keep the system working.
Finally, U.S. Published Application No. 2013/0071193 describes a small cartridge, which less parts and a stiff mechanism. This mechanism has the follow disadvantages:
(1) The adjustment process changes the lead angle, so applying this mechanism to blind holes is limited.
(2) The resolution is only 0.005 mm (5 μm).
(3) To make the adjustment more reliable, it is necessary to use or a gage, or a device with a light projection device.
Therefore, there is a need to provide a mechanism that solves the negative aspects described above.